An isolated gate-electrode of an insulated-gate bipolar transistor (IGBT) may form a capacitor (e.g., a gate capacitor or gate capacitance), which may have to be charged or discharged each time the IGBT is switched on or off. As a transistor may require a particular gate voltage in order to switch on, the gate capacitor may have to be charged to at least the required gate voltage for the transistor to be switched on. Similarly, to switch the transistor off, this voltage must be dissipated.
When such a transistor is switched on or off, it does not immediately switch from a non-conducting to a conducting state. The transistor may first have to overcome a certain amount of resistance. This resistance may be a function of the above-mentioned gate capacitance. Consequently, when a switching signal is applied to the transistor gate, a certain amount of heat may be generated which may be enough to destroy the transistor. Therefore, it may be beneficial to keep the switching time as short as possible, so as to minimize switching loss. Switching times may be in the range of microseconds and even nanoseconds. The switching time of a transistor may be inversely proportional to the amount of current used to charge the gate. Therefore, switching currents may be required in the range of, e.g., several hundred milliamperes, or even in the range of amperes. For typical gate voltages, approximately 10-15V, several watts of power may be required to drive the switch.
The switching signal for a transistor may be generated by a logic circuit or a microcontroller. The logic circuit or the microcontroller may provide an output signal that typically is limited to a few milliamperes of current. This is insufficient current, which may cause a power transistor gate to draw current too quickly such that it causes a current overdraw in the logic circuit or microcontroller and possible damage. To prevent this from happening, a gate drive is provided between the microcontroller output signal and a power transistor (e.g., an IGBT or MOSFET).
Typically, such a gate drive is provided with a dual power supply for facilitating switching an IGBT on and off.